1. Field of the Invention
The present invention generally relates to a gas-impermeable resinous composition and particularly to such composition used for forming members or parts which are required to have an excellent flexibility and heat resistance together with a high gas impermeability.
2. Discussion of the Prior Art
Conventionally resin such as nylon 6 has been used for forming members or parts which are required to have high gas impermeability. However, the nylon 6 and other gas-impermeable resins are comparatively rigid, and therefore such materials are not suitable for forming members which are additionally required to have high flexibility.
Referring to FIG. 5 there is shown a conventional refrigerant-transporting hose used as piping of car coolers, air conditioners and the like of automotive vehicles. The hose has a three-laminated or -layered structure consisting of an inner and an outer rubber tube 101, 103 and a reinforcing fiber layer 102 interposed between the inner and outer tubes 101, 103. The rubber hose has a high flexibility and therefore is handled with ease, for example in providing a refrigerant-using device with piping. On the other hand, rubber materials have a comparatively high gas permeability, that is, a comparatively low gas impermeability. Thus, the rubber hose suffers from the problem of progressive leakage of the refrigerant gas conveyed therethrough. Accordingly, it is necessary to often charge the refrigerant-using device with the refrigerant for compensating for lost fractions to maintain an optimum cooling capacity of the device. It goes without saying that is very troublesome.
There is a tendency that refrigerant discharged from the compressor of a cooling system for an automotive engine has raised temperature, which tendency results from raised speed of rotation of the engine. There is also a tendency that ambient air around an engine has increased temperature, which tendency results from small-sized engine room. Thus, it is necessary that refrigerant transporting hoses have excellent heat resistance. However, the above-mentioned conventional rubber hose has the problem that cracks are likely to be produced in the inner rubber tube if the hose is used at raised temperatures for a long period of time. That is, the hose does not have a reliable quality. In the case where hoses are formed of rubber material with high heat resistance, then such rubber material has an unsatisfactory gas impermeability, resulting in hoses produced with a low gas impermeability when compared with the above-mentioned conventional hose.
In the background described above, it has been proposed to form the inner tube of a hose of a resin which is excellent in both gas impermeability and heat resistance, in place of or in combination with rubber. However, in the case where nylon 6 is used as the resin, the material has a very high rigidity, and when used for producing hoses the material extremely lowers the flexibility of the hoses produced. Thus, nylon 6 is not suitable for practical use. In the case where a resin with a lower rigidity, such as nylon 6-66 copolymer and nylon 6-12 copolymer, is used to improve the flexibility of hoses, such resins have a melting point considerably lower than nylon 6 and do not satisfy the requirement of sufficient heat resistance.
The conventional gas-impermeable resins are unsatisfactory with regard to flexibility, and the resins with increased flexibility suffer from low heat resistance. Thus, none of the conventional resins have been suitable as material for forming members, such as refrigerant-transporting hoses, packings or the like, which are required to have high flexibility and heat resistance together with high gas impermeability.